File: rfc9253.html

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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 9253: Support for iCalendar Relationships</title>
<meta content="Michael Douglass" name="author">
<meta content="
       
        This specification updates the iCalendar RELATED-TO property
        defined in RFC 5545
        by adding new relation types and introduces new iCalendar
        properties (LINK, CONCEPT, and REFID) to allow better
        linking and grouping of iCalendar components and related data.
       
    " name="description">
<meta content="xml2rfc 3.14.0" name="generator">
<meta content="iCalendar" name="keyword">
<meta content="link" name="keyword">
<meta content="related-to" name="keyword">
<meta content="relationships" name="keyword">
<meta content="9253" name="rfc.number">
<!-- Generator version information:
  xml2rfc 3.14.0
    Python 3.9.13
    appdirs 1.4.4
    ConfigArgParse 1.5.3
    google-i18n-address 2.5.1
    html5lib 1.1
    intervaltree 3.1.0
    Jinja2 3.1.2
    kitchen 1.2.6
    lxml 4.9.0
    MarkupSafe 2.1.1
    pycountry 22.3.5
    PyYAML 6.0
    requests 2.28.0
    setuptools 44.1.1
    six 1.16.0
    weasyprint 56.1
-->
<link href="rfc9253.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  border: none;
  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
  margin: 0;
}
ul.empty, .ulEmpty {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
ul.ulBare, li.ulBare {
  margin-left: 0em !important;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
/* Fix PDF info block run off issue */
@media print {
  #identifiers dd {
    float: none;
  }
}
#identifiers .authors .author {
  display: inline-block;
  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  pre.breakable {
    break-inside: auto;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The follwing is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre, code {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
}
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<table class="ears">
<thead><tr>
<td class="left">RFC 9253</td>
<td class="center">iCalendar Relationships</td>
<td class="right">August 2022</td>
</tr></thead>
<tfoot><tr>
<td class="left">Douglass</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc9253" class="eref">9253</a></dd>
<dt class="label-updates">Updates:</dt>
<dd class="updates">
<a href="https://www.rfc-editor.org/rfc/rfc5545" class="eref">5545</a> </dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2022-08" class="published">August 2022</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Author:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">M. Douglass</div>
<div class="org">Bedework</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 9253</h1>
<h1 id="title">Support for iCalendar Relationships</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">
        This specification updates the iCalendar RELATED-TO property
        defined in RFC 5545
        by adding new relation types and introduces new iCalendar
        properties (LINK, CONCEPT, and REFID) to allow better
        linking and grouping of iCalendar components and related data.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc9253">https://www.rfc-editor.org/info/rfc9253</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2022 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.1">
                <p id="section-toc.1-1.1.2.1.1" class="keepWithNext"><a href="#section-1.1" class="xref">1.1</a>.  <a href="#name-structured-icalendar-relati" class="xref">Structured iCalendar Relationships</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.2">
                <p id="section-toc.1-1.1.2.2.1" class="keepWithNext"><a href="#section-1.2" class="xref">1.2</a>.  <a href="#name-grouped-icalendar-relations" class="xref">Grouped iCalendar Relationships</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.3">
                <p id="section-toc.1-1.1.2.3.1" class="keepWithNext"><a href="#section-1.3" class="xref">1.3</a>.  <a href="#name-concept-relationships" class="xref">Concept Relationships</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.4">
                <p id="section-toc.1-1.1.2.4.1"><a href="#section-1.4" class="xref">1.4</a>.  <a href="#name-linked-relationships" class="xref">Linked Relationships</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.5">
                <p id="section-toc.1-1.1.2.5.1"><a href="#section-1.5" class="xref">1.5</a>.  <a href="#name-caching-and-offline-use" class="xref">Caching and Offline Use</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.6">
                <p id="section-toc.1-1.1.2.6.1"><a href="#section-1.6" class="xref">1.6</a>.  <a href="#name-conventions-used-in-this-do" class="xref">Conventions Used in This Document</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-link-property-reference-typ" class="xref">LINK Property Reference Types</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-link-relation-types" class="xref">Link Relation Types</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-new-temporal-reltype-parame" class="xref">New Temporal RELTYPE Parameter Values</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-additional-new-reltype-para" class="xref">Additional New RELTYPE Parameter Values</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-new-property-parameters" class="xref">New Property Parameters</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-link-relation" class="xref">Link Relation</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-gap" class="xref">Gap</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-new-value-data-types" class="xref">New Value Data Types</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-new-properties" class="xref">New Properties</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8.2.1">
                <p id="section-toc.1-1.8.2.1.1"><a href="#section-8.1" class="xref">8.1</a>.  <a href="#name-concept" class="xref">Concept</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8.2.2">
                <p id="section-toc.1-1.8.2.2.1"><a href="#section-8.2" class="xref">8.2</a>.  <a href="#name-link" class="xref">Link</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8.2.3">
                <p id="section-toc.1-1.8.2.3.1"><a href="#section-8.3" class="xref">8.3</a>.  <a href="#name-refid" class="xref">Refid</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-updates-to-rfc-5545" class="xref">Updates to RFC 5545</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9.2.1">
                <p id="section-toc.1-1.9.2.1.1"><a href="#section-9.1" class="xref">9.1</a>.  <a href="#name-related-to" class="xref">RELATED-TO</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-10" class="xref">10</a>. <a href="#name-security-considerations" class="xref">Security Considerations</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-11" class="xref">11</a>. <a href="#name-iana-considerations" class="xref">IANA Considerations</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11.2.1">
                <p id="section-toc.1-1.11.2.1.1"><a href="#section-11.1" class="xref">11.1</a>.  <a href="#name-icalendar-property-registra" class="xref">iCalendar Property Registrations</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11.2.2">
                <p id="section-toc.1-1.11.2.2.1"><a href="#section-11.2" class="xref">11.2</a>.  <a href="#name-icalendar-property-paramete" class="xref">iCalendar Property Parameter Registrations</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11.2.3">
                <p id="section-toc.1-1.11.2.3.1"><a href="#section-11.3" class="xref">11.3</a>.  <a href="#name-icalendar-value-data-type-r" class="xref">iCalendar Value Data Type Registrations</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11.2.4">
                <p id="section-toc.1-1.11.2.4.1"><a href="#section-11.4" class="xref">11.4</a>.  <a href="#name-icalendar-reltype-value-reg" class="xref">iCalendar RELTYPE Value Registrations</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.12">
            <p id="section-toc.1-1.12.1"><a href="#section-12" class="xref">12</a>. <a href="#name-references" class="xref">References</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.12.2.1">
                <p id="section-toc.1-1.12.2.1.1"><a href="#section-12.1" class="xref">12.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.12.2.2">
                <p id="section-toc.1-1.12.2.2.1"><a href="#section-12.2" class="xref">12.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.13">
            <p id="section-toc.1-1.13.1"><a href="#appendix-A" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.14">
            <p id="section-toc.1-1.14.1"><a href="#appendix-B" class="xref"></a><a href="#name-authors-address" class="xref">Author's Address</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">
        iCalendar entities defined in <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> often
        need to be related to each other or to
        associated metadata. The specifications below support
        relationships of the following forms:<a href="#section-1-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-1-2">
        <dt id="section-1-2.1">Structured iCalendar:</dt>
        <dd style="margin-left: 1.5em" id="section-1-2.2">
            iCalendar entities can be related to each other in some structured
            way, for example, as parent, sibling, before, or after.<a href="#section-1-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-1-2.3">Grouped iCalendar:</dt>
        <dd style="margin-left: 1.5em" id="section-1-2.4">
            iCalendar entities can be related to each other as a group.
            CATEGORIES are often used for this purpose but are problematic
            for application developers due to their lack of consistency
            and use as a free-form tag.<a href="#section-1-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-1-2.5">Linked:</dt>
        <dd style="margin-left: 1.5em" id="section-1-2.6">
            Entities can be linked to other entities, such as vCards,
            through a URI and associated REL and FMTTYPE parameters.<a href="#section-1-2.6" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<section id="section-1.1">
        <h3 id="name-structured-icalendar-relati">
<a href="#section-1.1" class="section-number selfRef">1.1. </a><a href="#name-structured-icalendar-relati" class="section-name selfRef">Structured iCalendar Relationships</a>
        </h3>
<p id="section-1.1-1">
          The iCalendar <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span>
          RELATED-TO property has no support for temporal relationships
          as used by project management tools.<a href="#section-1.1-1" class="pilcrow">¶</a></p>
<p id="section-1.1-2">
          The RELTYPE parameter is extended to take new values
          defining temporal relationships, a GAP parameter is defined to provide
          lead and lag values, and RELATED-TO is extended to allow URI values.
          These changes allow the RELATED-TO property to define a richer set of
          relationships useful for project management.<a href="#section-1.1-2" class="pilcrow">¶</a></p>
</section>
<section id="section-1.2">
        <h3 id="name-grouped-icalendar-relations">
<a href="#section-1.2" class="section-number selfRef">1.2. </a><a href="#name-grouped-icalendar-relations" class="section-name selfRef">Grouped iCalendar Relationships</a>
        </h3>
<p id="section-1.2-1">
          This specification defines a new REFID property, which
          allows arbitrary groups of entities to be associated with the same
          key value.<a href="#section-1.2-1" class="pilcrow">¶</a></p>
<p id="section-1.2-2">
          REFID is used to identify a key allowing the association of
          components that are all related to the referring, aggregating
          component and the retrieval of components based on this key.
          For example, this may be used to identify the tasks associated
          with a given project without having to communicate the task
          structure of the project. A further example is the grouping
          of all sub-tasks associated with the delivery of a specific
          package in a package delivery system.<a href="#section-1.2-2" class="pilcrow">¶</a></p>
<p id="section-1.2-3">
          As such, the presence of a REFID property imparts no meaning
          to the component. It is merely a key to allow retrieval. This is
          distinct from categorization, which, while allowing grouping,
          also adds meaning to the component to which it is attached.<a href="#section-1.2-3" class="pilcrow">¶</a></p>
</section>
<section id="section-1.3">
        <h3 id="name-concept-relationships">
<a href="#section-1.3" class="section-number selfRef">1.3. </a><a href="#name-concept-relationships" class="section-name selfRef">Concept Relationships</a>
        </h3>
<p id="section-1.3-1">
          The name CONCEPT is used by the Simple Knowledge Organization
          System, as defined in <span>[<a href="#W3C.REC-skos-reference-20090818" class="xref">W3C.REC-skos-reference-20090818</a>]</span>.
          The term "concept" more accurately defines what we often
          mean by a category. It's not the text string that is important
          but the meaning attached to it. For example, the term
          "football" can mean very different sports.<a href="#section-1.3-1" class="pilcrow">¶</a></p>
<p id="section-1.3-2">
          The introduction of CONCEPT allows a more structured
          approach to categorization, with the possibility of namespaced
          and path-like values. Unlike REFID, the CONCEPT property imparts some
          meaning. It is assumed that the value of this property will
          reference a well-defined category.<a href="#section-1.3-2" class="pilcrow">¶</a></p>
<p id="section-1.3-3">
          The current CATEGORIES property defined in <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> is used
          as a free-form 'tagging' field. These values have some meaning
          to those who apply them but not necessarily to any consumer.
          As such, it is difficult to establish
          formal relationships between components based on their category.<a href="#section-1.3-3" class="pilcrow">¶</a></p>
<p id="section-1.3-4">
          Rather than attempt to add semantics to the CATEGORIES property,
          it seems best to continue its usage as an informal tag and
          establish a new CONCEPT property with more constraints.<a href="#section-1.3-4" class="pilcrow">¶</a></p>
</section>
<section id="section-1.4">
        <h3 id="name-linked-relationships">
<a href="#section-1.4" class="section-number selfRef">1.4. </a><a href="#name-linked-relationships" class="section-name selfRef">Linked Relationships</a>
        </h3>
<p id="section-1.4-1">
          The currently existing iCalendar standard <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> lacks
          a general purpose method for referencing additional, external information
          relating to calendar components.<a href="#section-1.4-1" class="pilcrow">¶</a></p>
<p id="section-1.4-2">
          This document proposes a method for referencing typed external
          information that can provide additional information about an iCalendar
          component. This new LINK property is closely aligned to
          <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>, which defines the generic concept
          of Web Linking, as well as its expression in the HTTP LINK header
          field.<a href="#section-1.4-2" class="pilcrow">¶</a></p>
<p id="section-1.4-3">
          The LINK property defines a typed reference or relation to external
          metadata or related resources. By providing type and format information
          as parameters, clients and servers are able to discover interesting
          references and make use of them, perhaps for indexing or the
          presentation of interesting links for the user.<a href="#section-1.4-3" class="pilcrow">¶</a></p>
<p id="section-1.4-4">
          Calendar components are often grouped into collections to represent a
          calendar or a series of tasks, for example, Calendaring Extensions to
   WebDAV (CalDAV) calendar collections <span>[<a href="#RFC4791" class="xref">RFC4791</a>]</span>.<a href="#section-1.4-4" class="pilcrow">¶</a></p>
<p id="section-1.4-5">
          It is also often necessary to reference calendar components
          in other collections. For example, a VEVENT might refer to
          a VTODO from which it was derived. The PARENT, SIBLING, and CHILD
          relationships defined for the
          RELATED-TO property only allow for a unique identifier (UID), which is inadequate for many
          purposes. Allowing other value types for those relationships may help
          but would cause
          backward-compatibility issues. The LINK property can link components
          in different collections or even on different servers.<a href="#section-1.4-5" class="pilcrow">¶</a></p>
<p id="section-1.4-6">
          When publishing events, it is useful to be able to refer back to the
          source of that information. The actual event may have been consumed from
          a feed or an ics file on a website. A LINK property can provide
          a reference to the originator of the event.<a href="#section-1.4-6" class="pilcrow">¶</a></p>
<p id="section-1.4-7">
          Beyond the need to relate elements temporally, project
          management tools often need to be able to specify the relationships
          between the various events and tasks that make up a project.
          The LINK property provides such a mechanism.<a href="#section-1.4-7" class="pilcrow">¶</a></p>
<p id="section-1.4-8">
          The LINK property <span class="bcp14">MUST NOT</span> be treated as just another
          attachment. The ATTACH property defined in
          <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> has been extended by
          <span>[<a href="#RFC8607" class="xref">RFC8607</a>]</span>
          to handle server-side management and stripping of inline data and to
          provide additional data about the attachment (size, filename, etc.).<a href="#section-1.4-8" class="pilcrow">¶</a></p>
<p id="section-1.4-9">
          Additionally, clients may choose to handle attachments differently
          from the LINK property, as attachments are often an integral part
          of the message, for example, the agenda.<a href="#section-1.4-9" class="pilcrow">¶</a></p>
</section>
<div id="caching">
<section id="section-1.5">
        <h3 id="name-caching-and-offline-use">
<a href="#section-1.5" class="section-number selfRef">1.5. </a><a href="#name-caching-and-offline-use" class="section-name selfRef">Caching and Offline Use</a>
        </h3>
<p id="section-1.5-1">
          In general, the calendar entity should be self explanatory
          without the need to download referenced metadata, such as a
          web page.<a href="#section-1.5-1" class="pilcrow">¶</a></p>
<p id="section-1.5-2">
          However, to facilitate offline display, the link type may identify
          important pieces of data that should be downloaded in
          advance.<a href="#section-1.5-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="conventions">
<section id="section-1.6">
        <h3 id="name-conventions-used-in-this-do">
<a href="#section-1.6" class="section-number selfRef">1.6. </a><a href="#name-conventions-used-in-this-do" class="section-name selfRef">Conventions Used in This Document</a>
        </h3>
<p id="section-1.6-1">
    The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>",
    "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL NOT</span>", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>",
    "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
    "<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are
    to be interpreted as described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span>
          <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> when, and only when, they appear in all capitals,
    as shown here.<a href="#section-1.6-1" class="pilcrow">¶</a></p>
<p id="section-1.6-2">
          The notation used in this memo to (re-)define iCalendar elements is
          the ABNF notation of <span>[<a href="#RFC5234" class="xref">RFC5234</a>]</span>, as used by
          <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span>.  Any syntax
          elements shown below that are not explicitly defined in this
          specification come from iCalendar [RFC5545].<a href="#section-1.6-2" class="pilcrow">¶</a></p>
</section>
</div>
</section>
<div id="link_reference_types">
<section id="section-2">
      <h2 id="name-link-property-reference-typ">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-link-property-reference-typ" class="section-name selfRef">LINK Property Reference Types</a>
      </h2>
<p id="section-2-1">
        The reference value in the LINK property defined below can take
        three forms specified by the VALUE parameter:<a href="#section-2-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-2">
        <dt id="section-2-2.1">URI:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.2">
            This is a URI referring to the target.<a href="#section-2-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.3">UID:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.4">
            This allows for linking within a single collection of calendar
            components, and the value <span class="bcp14">MUST</span> refer to another component
            within the same collection.<a href="#section-2-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.5">XML-REFERENCE:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.6">
            In an XML environment, it may be necessary to refer to a
            fragment of an external XML artifact. This value is a URI
            with an XPointer anchor value. The XPointer is defined in
            <span>[<a href="#W3C.WD-xptr-xpointer-20021219" class="xref">W3C.WD-xptr-xpointer-20021219</a>]</span>, and its
            use as an anchor is defined in <span>[<a href="#W3C.REC-xptr-framework-20030325" class="xref">W3C.REC-xptr-framework-20030325</a>]</span>.<a href="#section-2-2.6" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-2-3">
        Note that UID references may need updating on import. An example
        is data to be imported from a file containing VTODO and VEVENT components,
        with a VTODO referring to VEVENT components by UID. When imported
        into a CalDAV system, the VTODO components are typically placed in a different
        collection from the VEVENT components. This would require the
        UID reference to be replaced with a URI.<a href="#section-2-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="link_relation_types">
<section id="section-3">
      <h2 id="name-link-relation-types">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-link-relation-types" class="section-name selfRef">Link Relation Types</a>
      </h2>
<p id="section-3-1">
        Two forms of relation types are defined in <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>: registered and
        extension.  Registered relation types are added to the "Link
        Relations" registry, as specified in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-2.1.1" class="relref">Section 2.1.1</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>.
        Extension relation types, defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-2.1.2" class="relref">Section 2.1.2</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>,
        are specified as unique URIs that are not registered in the registry.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">
        The relation types defined in <a href="#linkrel" class="xref">Section 6.1</a> will
        be registered with IANA in
        accordance with the specifications in  <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-3-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="new_temporal_reltype_values">
<section id="section-4">
      <h2 id="name-new-temporal-reltype-parame">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-new-temporal-reltype-parame" class="section-name selfRef">New Temporal RELTYPE Parameter Values</a>
      </h2>
<p id="section-4-1">
        This section defines the usual temporal relationships
        for use with the RELTYPE parameter defined in
        <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.2.15" class="relref">Section 3.2.15</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>:
        FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH, or STARTTOSTART.<a href="#section-4-1" class="pilcrow">¶</a></p>
<p id="section-4-2">
        The <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> RELATED-TO property with one or
        more of these temporal relationships will be present in the
        predecessor entity and will refer to the successor entity.<a href="#section-4-2" class="pilcrow">¶</a></p>
<p id="section-4-3">
        The GAP parameter (see <a href="#gap" class="xref">Section 6.2</a>)
        specifies the lead (a negative value) or lag (a positive value)
        time between the predecessor and the successor.<a href="#section-4-3" class="pilcrow">¶</a></p>
<p id="section-4-4">
        In the description of each temporal relationship
        below, we refer to Task-A, which contains and controls the relationship, and
        Task-B, which is the target of the relationship. This is indicated by
        the direction of the arrows in the diagrams below.<a href="#section-4-4" class="pilcrow">¶</a></p>
<p id="section-4-5">
        Also, each relationship may be modified by the addition of a
        GAP parameter to the relationship that applies to the targeted
        component.<a href="#section-4-5" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-4-6">
        <dt id="section-4-6.1">RELTYPE=FINISHTOSTART:</dt>
        <dd style="margin-left: 1.5em" id="section-4-6.2">
          <p id="section-4-6.2.1">
            Task-B cannot start until Task-A finishes.
            For example, when painting is complete, carpet laying can begin.<a href="#section-4-6.2.1" class="pilcrow">¶</a></p>
<span id="name-finish-to-start-relationshi"></span><div id="finishtostart">
<figure id="figure-1">
            <div class="alignLeft art-text artwork" id="section-4-6.2.2.1">
<pre>
            ============
            |  Task-A  |
            ============
                       |
                       V
                       ============
                       |  Task-B  |
                       ============
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-finish-to-start-relationshi" class="selfRef">Finish-to-Start Relationship</a>
            </figcaption></figure>
</div>
</dd>
        <dd class="break"></dd>
<dt id="section-4-6.3">RELTYPE=FINISHTOFINISH:</dt>
        <dd style="margin-left: 1.5em" id="section-4-6.4">
          <p id="section-4-6.4.1">Task-B can only be completed after Task-A
            is finished. The related tasks may run in parallel before
            completion.<a href="#section-4-6.4.1" class="pilcrow">¶</a></p>
<p id="section-4-6.4.2">
            For example, in the development of two related pieces of
            software (e.g., the API and the implementation), the design
            of the implementation (Task-B) cannot be completed until the
            design of the API (Task-A) has been completed.<a href="#section-4-6.4.2" class="pilcrow">¶</a></p>
<span id="name-finish-to-finish-relationsh"></span><div id="finishtofinish">
<figure id="figure-2">
            <div class="alignLeft art-text artwork" id="section-4-6.4.3.1">
<pre>
                    ==================
                    |     Task-A     |--+
                    ==================  |
                                        |
                          ============  |
                          |  Task-B  |&lt;-+
                          ============
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-finish-to-finish-relationsh" class="selfRef">Finish-to-Finish Relationship</a>
            </figcaption></figure>
</div>
</dd>
        <dd class="break"></dd>
<dt id="section-4-6.5">RELTYPE=STARTTOFINISH:</dt>
        <dd style="margin-left: 1.5em" id="section-4-6.6">
          <p id="section-4-6.6.1">
            The start of Task-A (which occurs after Task-B)
            controls the finish of Task-B.
            For example, ticket sales (Task-B) end after the game
            starts (Task-A).<a href="#section-4-6.6.1" class="pilcrow">¶</a></p>
<span id="name-start-to-finish-relationshi"></span><div id="starttofinish">
<figure id="figure-3">
            <div class="alignLeft art-text artwork" id="section-4-6.6.2.1">
<pre>
                           ============
                        +--|  Task-A  |
                        |  ============
                        +---------+
                    ============  |
                    |  Task-B  |&lt;-+
                    ============
</pre>
</div>
<figcaption><a href="#figure-3" class="selfRef">Figure 3</a>:
<a href="#name-start-to-finish-relationshi" class="selfRef">Start-to-Finish Relationship</a>
            </figcaption></figure>
</div>
</dd>
        <dd class="break"></dd>
<dt id="section-4-6.7">RELTYPE=STARTTOSTART:</dt>
        <dd style="margin-left: 1.5em" id="section-4-6.8">
          <p id="section-4-6.8.1">
            The start of Task-A triggers the start of Task-B,
            that is, Task-B can start anytime after Task-A starts.<a href="#section-4-6.8.1" class="pilcrow">¶</a></p>
<span id="name-start-to-start-relationship"></span><div id="starttostart">
<figure id="figure-4">
            <div class="alignLeft art-text artwork" id="section-4-6.8.2.1">
<pre>
                    ============
                 +--|  Task-A  |
                 |  ============
                 |
                 |  ============
                 +-&gt;|  Task-B  |
                    ============
</pre>
</div>
<figcaption><a href="#figure-4" class="selfRef">Figure 4</a>:
<a href="#name-start-to-start-relationship" class="selfRef">Start-to-Start Relationship</a>
            </figcaption></figure>
</div>
</dd>
      <dd class="break"></dd>
</dl>
</section>
</div>
<div id="additional_new_reltype_values">
<section id="section-5">
      <h2 id="name-additional-new-reltype-para">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-additional-new-reltype-para" class="section-name selfRef">Additional New RELTYPE Parameter Values</a>
      </h2>
<p id="section-5-1">
        This section defines the additional relationships below:<a href="#section-5-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-5-2">
        <dt id="section-5-2.1">RELTYPE=FIRST:</dt>
        <dd style="margin-left: 1.5em" id="section-5-2.2">
            This indicates that the referenced calendar component is the
            first in a series the referencing calendar component is
            part of.<a href="#section-5-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-5-2.3">RELTYPE=NEXT:</dt>
        <dd style="margin-left: 1.5em" id="section-5-2.4">
            This indicates that the referenced calendar component is the
            next in a series the referencing calendar component is
            part of.<a href="#section-5-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-5-2.5">RELTYPE=DEPENDS-ON:</dt>
        <dd style="margin-left: 1.5em" id="section-5-2.6">
            This indicates that the current calendar component depends on
            the referenced calendar component in some manner. For example,
            a task may be blocked waiting on the other, referenced, task.<a href="#section-5-2.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-5-2.7">RELTYPE=REFID:</dt>
        <dd style="margin-left: 1.5em" id="section-5-2.8">
            This establishes a reference from the current component to
            components with a REFID property that matches the value
            given in the associated RELATED-TO property.<a href="#section-5-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-5-2.9">RELTYPE=CONCEPT:</dt>
        <dd style="margin-left: 1.5em" id="section-5-2.10">
            This establishes a reference from the current component to
            components with a CONCEPT property that matches the value
            given in the associated RELATED-TO property.<a href="#section-5-2.10" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-5-3">
        Note that the relationship types of PARENT, CHILD, and SIBLING
        establish a hierarchical relationship. The new types of FIRST
        and NEXT are an ordering relationship.<a href="#section-5-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="new_property_parameters">
<section id="section-6">
      <h2 id="name-new-property-parameters">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-new-property-parameters" class="section-name selfRef">New Property Parameters</a>
      </h2>
<div id="linkrel">
<section id="section-6.1">
        <h3 id="name-link-relation">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-link-relation" class="section-name selfRef">Link Relation</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.1-1">
          <dt id="section-6.1-1.1">Parameter name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.2">
              LINKREL<a href="#section-6.1-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.4">
              This property specifies the relationship of data referenced by a LINK property.<a href="#section-6.1-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.5">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.6">
            <p id="section-6.1-1.6.1" class="keepWithNext">
                  This parameter is defined by the following notation:<a href="#section-6.1-1.6.1" class="pilcrow">¶</a></p>
<div id="section-6.1-1.6.2">
<pre class="lang-abnf sourcecode">
linkrelparam = "LINKREL" "="
                (DQUOTE uri DQUOTE
               / iana-token)   ; Other IANA registered type
</pre><a href="#section-6.1-1.6.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.7">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.8">
            <p id="section-6.1-1.8.1">This parameter <span class="bcp14">MUST</span> be specified on all LINK properties and
              define the type of reference. This allows programs consuming this
              data to automatically scan for references they support. There is no default
       relation type.<a href="#section-6.1-1.8.1" class="pilcrow">¶</a></p>
<p id="section-6.1-1.8.2">Any link relation 
              in the link registry established by <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>,
              or new link relations, may be used.
              It is expected that link relation types seeing significant
              usage in calendaring will have the calendaring usage
              described in an RFC.<a href="#section-6.1-1.8.2" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.9">LINKREL=latest-version:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.10">
     This identifies the latest version of the event information.<a href="#section-6.1-1.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.1-1.11">Registration:</dt>
          <dd style="margin-left: 1.5em" id="section-6.1-1.12">
              These relation types are registered in <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-6.1-1.12" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="gap">
<section id="section-6.2">
        <h3 id="name-gap">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-gap" class="section-name selfRef">Gap</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-6.2-1">
          <dt id="section-6.2-1.1">Parameter name:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.2">
              GAP<a href="#section-6.2-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.4">
              This property specifies the length of the gap, positive or negative,
              between two components with a temporal relationship.<a href="#section-6.2-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.5">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.6">
            <p id="section-6.2-1.6.1" class="keepWithNext">
                  This parameter is defined by the following notation, where
                  dur-value is defined in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.3.6" class="relref">Section 3.3.6</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>. :<a href="#section-6.2-1.6.1" class="pilcrow">¶</a></p>
<div id="section-6.2-1.6.2">
<pre class="lang-abnf sourcecode">
  gapparam      = "GAP" "=" dur-value
</pre><a href="#section-6.2-1.6.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-6.2-1.7">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-6.2-1.8">
            <p id="section-6.2-1.8.1">This parameter <span class="bcp14">MAY</span> be specified on the RELATED-TO property and
              defines the duration of time between the predecessor and successor
              in an interval. When positive, it defines the lag time between
              a task and its logical successor. When negative, it defines
              the lead time.<a href="#section-6.2-1.8.1" class="pilcrow">¶</a></p>
<p id="section-6.2-1.8.2">
              An example of lag time might be if Task-A is "paint the room"
              and Task-B is
              "lay the carpets". Then, Task-A may be related to Task-B with
              RELTYPE=FINISHTOSTART with a gap of 1 day -- long enough for the paint to
              dry.<a href="#section-6.2-1.8.2" class="pilcrow">¶</a></p>
<span id="name-finish-to-start-relationship"></span><div id="finishtostart-lag">
<figure id="figure-5">
              <div class="alignLeft art-text artwork" id="section-6.2-1.8.3.1">
<pre>
            ====================
            |  paint the room  |--+
            ====================  |
                                  |(lag of one day)
                                  |
                                  |  ===================
                                  +-&gt;| lay the carpet  |
                                     ===================
</pre>
</div>
<figcaption><a href="#figure-5" class="selfRef">Figure 5</a>:
<a href="#name-finish-to-start-relationship" class="selfRef">Finish-to-Start Relationship with Lag</a>
              </figcaption></figure>
</div>
<p id="section-6.2-1.8.4">
              For an example of lead time, in constructing a two-story
              building, the electrical work must be done before painting.
              However, the painter can move in to the first floor as the
              electricians move upstairs.<a href="#section-6.2-1.8.4" class="pilcrow">¶</a></p>
<span id="name-finish-to-start-relationship-"></span><div id="finishtostart-lead">
<figure id="figure-6">
              <div class="alignLeft art-text artwork" id="section-6.2-1.8.5.1">
<pre>
            =====================
            |  electrical work  |--+
            =====================  |
                     +-------------+
                     |(lead of estimated time)
                     |  ==================
                     +-&gt;|    painting    |
                        ==================
</pre>
</div>
<figcaption><a href="#figure-6" class="selfRef">Figure 6</a>:
<a href="#name-finish-to-start-relationship-" class="selfRef">Finish-to-Start Relationship with Lead</a>
              </figcaption></figure>
</div>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
</section>
</div>
<div id="new_value_data_types">
<section id="section-7">
      <h2 id="name-new-value-data-types">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-new-value-data-types" class="section-name selfRef">New Value Data Types</a>
      </h2>
<p id="section-7-1">
        This specification defines the following new value types to
        be used with the VALUE property parameter:<a href="#section-7-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-7-2">
        <dt id="section-7-2.1">UID:</dt>
        <dd style="margin-left: 1.5em" id="section-7-2.2">
            VALUE=UID indicates that the associated value is the UID for a
            component.<a href="#section-7-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-7-2.3">XML-REFERENCE:</dt>
        <dd style="margin-left: 1.5em" id="section-7-2.4">
            VALUE=XML-REFERENCE indicates that the associated value
            references an associated XML artifact and is a URI
            with an XPointer anchor value. The XPointer is defined in
            <span>[<a href="#W3C.WD-xptr-xpointer-20021219" class="xref">W3C.WD-xptr-xpointer-20021219</a>]</span>, and its
            use as an anchor is defined in <span>[<a href="#W3C.REC-xptr-framework-20030325" class="xref">W3C.REC-xptr-framework-20030325</a>]</span>.<a href="#section-7-2.4" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
</section>
</div>
<div id="new_properties">
<section id="section-8">
      <h2 id="name-new-properties">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-new-properties" class="section-name selfRef">New Properties</a>
      </h2>
<div id="concept">
<section id="section-8.1">
        <h3 id="name-concept">
<a href="#section-8.1" class="section-number selfRef">8.1. </a><a href="#name-concept" class="section-name selfRef">Concept</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-8.1-1">
          <dt id="section-8.1-1.1">Property name:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.2">
              CONCEPT<a href="#section-8.1-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.4">
              This property defines the formal categories for a calendar
              component.<a href="#section-8.1-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.5">Value type:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.6">
              URI<a href="#section-8.1-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.7">Property Parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.8">
              IANA and non-standard parameters can be specified on this property.<a href="#section-8.1-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.9">Conformance:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.10">
              This property can be specified zero or more times in any
              iCalendar component.<a href="#section-8.1-1.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.11">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.12">
            <p id="section-8.1-1.12.1">This property is used to specify formal categories or
              classifications of the calendar component.  The values
              are useful in searching for a calendar component of a
              particular type and category.<a href="#section-8.1-1.12.1" class="pilcrow">¶</a></p>
<p id="section-8.1-1.12.2">This categorization is distinct from the more informal
              "tagging" of components provided by the existing CATEGORIES
              property. It is expected that the value of the CONCEPT
              property will reference an external resource that
              provides information about the categorization.<a href="#section-8.1-1.12.2" class="pilcrow">¶</a></p>
<p id="section-8.1-1.12.3">In addition, a structured URI value allows for
              hierarchical categorization of events.<a href="#section-8.1-1.12.3" class="pilcrow">¶</a></p>
<p id="section-8.1-1.12.4">Possible category resources are the various proprietary
              systems, for example, the Library of Congress, or an open
              source of categorization data.<a href="#section-8.1-1.12.4" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.13">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.14">
            <p id="section-8.1-1.14.1" class="keepWithNext">
                  This property is defined by the following notation:<a href="#section-8.1-1.14.1" class="pilcrow">¶</a></p>
<div id="section-8.1-1.14.2">
<pre class="lang-abnf sourcecode">
  concept        =  "CONCEPT" conceptparam ":"
                        uri CRLF

  conceptparam = *(";" other-param)
</pre><a href="#section-8.1-1.14.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-8.1-1.15">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-8.1-1.16">
            <p id="section-8.1-1.16.1" class="keepWithNext">
                  The following is an example of this property. It points to a
                  server acting as the source for the calendar object.<a href="#section-8.1-1.16.1" class="pilcrow">¶</a></p>
<div id="section-8.1-1.16.2">
<pre class="sourcecode">
  CONCEPT:https://example.com/event-types/arts/music
</pre><a href="#section-8.1-1.16.2" class="pilcrow">¶</a>
</div>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="link">
<section id="section-8.2">
        <h3 id="name-link">
<a href="#section-8.2" class="section-number selfRef">8.2. </a><a href="#name-link" class="section-name selfRef">Link</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-8.2-1">
          <dt id="section-8.2-1.1">Property name:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.2">
              LINK<a href="#section-8.2-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.4">
              This property provides a reference to external information
              related to a component.<a href="#section-8.2-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.5">Value type:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.6">
              URI, UID, or XML-REFERENCE<a href="#section-8.2-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.7">Property Parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.8">
              The VALUE parameter is required. Non-standard, link relation type,
              format type, label, and language parameters can also be
              specified on this property. The LABEL parameter
              is defined in <span>[<a href="#RFC7986" class="xref">RFC7986</a>]</span>.<a href="#section-8.2-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.9">Conformance:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.10">
              This property can be specified zero or more times in any
              iCalendar component.<a href="#section-8.2-1.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.11">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.12">
              When used in a component, the value of this property points to
              additional information related to the component. For example,
              it may reference the originating web server.<a href="#section-8.2-1.12" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.13">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.14">
            <p id="section-8.2-1.14.1" class="keepWithNext">
                  This property is defined by the following notation:<a href="#section-8.2-1.14.1" class="pilcrow">¶</a></p>
<div id="section-8.2-1.14.2">
<pre class="lang-abnf sourcecode">
   link           = "LINK" linkparam ":"
                      ( uri /  ; for VALUE=XML-REFERENCE
                        uri /  ; for VALUE=URI
                        text ) ; for VALUE=UID
                    CRLF

   linkparam      = (";" "VALUE" "=" ("XML-REFERENCE" /
                                "URI" /
                                "UID"))
                    1*(";" linkrelparam)
                    1*(";" fmttypeparam)
                    1*(";" labelparam)
                    1*(";" languageparam)
                    *(";" other-param)
                    ; the elements herein may appear in any order,
                    ; and the order is not significant.
</pre><a href="#section-8.2-1.14.2" class="pilcrow">¶</a>
</div>
<p id="section-8.2-1.14.3">This property is a serialization of the model in
              <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>, where the link target is
              carried in the property value, the link context is the
              containing calendar entity, and the link relation type
              and any target attributes are carried in iCalendar property
              parameters.<a href="#section-8.2-1.14.3" class="pilcrow">¶</a></p>
<p id="section-8.2-1.14.4">
              The LINK property parameters
              map to <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span> attributes as follows:<a href="#section-8.2-1.14.4" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-8.2-1.14.5">
              <dt id="section-8.2-1.14.5.1">LABEL:</dt>
              <dd style="margin-left: 1.5em" id="section-8.2-1.14.5.2">
                  This parameter maps to the "title" attribute defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-3.4.1" class="relref">Section 3.4.1</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-8.2-1.14.5.2" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.2-1.14.5.3">LANGUAGE:</dt>
              <dd style="margin-left: 1.5em" id="section-8.2-1.14.5.4">
                  This parameter maps to the "hreflang" attribute defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-3.4.1" class="relref">Section 3.4.1</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-8.2-1.14.5.4" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.2-1.14.5.5">LINKREL:</dt>
              <dd style="margin-left: 1.5em" id="section-8.2-1.14.5.6">
                  This parameter maps to the link relation type defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-2.1" class="relref">Section 2.1</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-8.2-1.14.5.6" class="pilcrow">¶</a>
</dd>
              <dd class="break"></dd>
<dt id="section-8.2-1.14.5.7">FMTTYPE:</dt>
              <dd style="margin-left: 1.5em" id="section-8.2-1.14.5.8">
                  This parameter maps to the "type" attribute defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8288#section-3.4.1" class="relref">Section 3.4.1</a> of [<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-8.2-1.14.5.8" class="pilcrow">¶</a>
</dd>
            <dd class="break"></dd>
</dl>
<p id="section-8.2-1.14.6">There is no mapping for "title*",
              "anchor", "rev", or "media" <span>[<a href="#RFC8288" class="xref">RFC8288</a>]</span>.<a href="#section-8.2-1.14.6" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.15">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.16">
            <p id="section-8.2-1.16.1" class="keepWithNext">
                  The following is an example of this property, which
                  provides a reference to the source for the calendar object.<a href="#section-8.2-1.16.1" class="pilcrow">¶</a></p>
<div id="section-8.2-1.16.2">
<pre class="sourcecode">
  LINK;LINKREL=SOURCE;LABEL=Venue;VALUE=URI:
   https://example.com/events
</pre><a href="#section-8.2-1.16.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.17">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.18">
            <p id="section-8.2-1.18.1" class="keepWithNext">
                  The following is an example of this property, which
                  provides a reference to an entity from which this one
                  was derived. The link relation is a vendor-defined value.<a href="#section-8.2-1.18.1" class="pilcrow">¶</a></p>
<div id="section-8.2-1.18.2">
<pre class="sourcecode">
  LINK;LINKREL="https://example.com/linkrel/derivedFrom";
   VALUE=URI:
   https://example.com/tasks/01234567-abcd1234.ics
</pre><a href="#section-8.2-1.18.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-8.2-1.19">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-8.2-1.20">
            <p id="section-8.2-1.20.1" class="keepWithNext">
                  The following is an example of this property, which
                  provides a reference to a fragment of an XML document.
                  The link relation is a vendor-defined value.<a href="#section-8.2-1.20.1" class="pilcrow">¶</a></p>
<div id="section-8.2-1.20.2">
<pre class="sourcecode">
  LINK;LINKREL="https://example.com/linkrel/costStructure";
   VALUE=XML-REFERENCE:
   https://example.com/xmlDocs/bidFramework.xml
   #xpointer(descendant::CostStruc/range-to(
   following::CostStrucEND[1]))
</pre><a href="#section-8.2-1.20.2" class="pilcrow">¶</a>
</div>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="refid">
<section id="section-8.3">
        <h3 id="name-refid">
<a href="#section-8.3" class="section-number selfRef">8.3. </a><a href="#name-refid" class="section-name selfRef">Refid</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-8.3-1">
          <dt id="section-8.3-1.1">Property name:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.2">
              REFID<a href="#section-8.3-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.4">
              This property value acts as a key for associated
              iCalendar entities.<a href="#section-8.3-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.5">Value type:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.6">
              TEXT<a href="#section-8.3-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.7">Property Parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.8">
              Non-standard parameters can be specified on this property.<a href="#section-8.3-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.9">Conformance:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.10">
              This property can be specified zero or more times in any
              iCalendar component.<a href="#section-8.3-1.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.11">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.12">
              The value of this property is free-form text that
              creates an identifier for associated components.  All components
              that use the same REFID value are associated through that value
              and can be located or retrieved as a group.  For example, all of
              the events in a travel itinerary would have the same REFID value,
              so as to be grouped together.<a href="#section-8.3-1.12" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.13">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.14">
            <p id="section-8.3-1.14.1" class="keepWithNext">
                  This property is defined by the following notation:<a href="#section-8.3-1.14.1" class="pilcrow">¶</a></p>
<div id="section-8.3-1.14.2">
<pre class="lang-abnf sourcecode">
  refid      = "REFID" refidparam ":" text CRLF


  refidparam      = *(";" other-param)

</pre><a href="#section-8.3-1.14.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-8.3-1.15">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-8.3-1.16">
            <p id="section-8.3-1.16.1" class="keepWithNext">
                  The following is an example of this property.<a href="#section-8.3-1.16.1" class="pilcrow">¶</a></p>
<div id="section-8.3-1.16.2">
<pre class="sourcecode">
  REFID:itinerary-2014-11-17
</pre><a href="#section-8.3-1.16.2" class="pilcrow">¶</a>
</div>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
</section>
</div>
<div id="updates_to_rfc_5545">
<section id="section-9">
      <h2 id="name-updates-to-rfc-5545">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-updates-to-rfc-5545" class="section-name selfRef">Updates to RFC 5545</a>
      </h2>
<p id="section-9-1">
        This specification updates the RELATED-TO property defined
        in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.8.4.5" class="relref">Section 3.8.4.5</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>. The contents
        of <a href="#related-to" class="xref">Section 9.1</a> replace that section.<a href="#section-9-1" class="pilcrow">¶</a></p>
<p id="section-9-2">
        The RELTYPE parameter is extended to take new values defining
        temporal relationships, a GAP parameter is defined to provide lead
        and lag values, and RELATED-TO is extended to allow URI values.
        These changes allow the RELATED-TO property to define a richer set of
        relationships useful for project management.<a href="#section-9-2" class="pilcrow">¶</a></p>
<div id="related-to">
<section id="section-9.1">
        <h3 id="name-related-to">
<a href="#section-9.1" class="section-number selfRef">9.1. </a><a href="#name-related-to" class="section-name selfRef">RELATED-TO</a>
        </h3>
<span class="break"></span><dl class="dlParallel" id="section-9.1-1">
          <dt id="section-9.1-1.1">Property name:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.2">
              RELATED-TO<a href="#section-9.1-1.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.3">Purpose:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.4">
              This property is used to represent a relationship or
              reference between one calendar component and another. The definition
              here extends the definition in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.8.4.5" class="relref">Section 3.8.4.5</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span> by allowing URI or UID values and a GAP parameter.<a href="#section-9.1-1.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.5">Value Type:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.6">
              URI, UID, or TEXT<a href="#section-9.1-1.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.7">Property Parameters:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.8">
              Relationship type, IANA, and non-standard
              property parameters can be specified on this property.<a href="#section-9.1-1.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.9">Conformance:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.10">
              This property <span class="bcp14">MAY</span> be specified in any iCalendar component.<a href="#section-9.1-1.10" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.11">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.12">
            <p id="section-9.1-1.12.1">By default or when VALUE=UID is specified, the property value
              consists of the persistent, globally
              unique identifier of another calendar component.  This value would
              be represented in a calendar component by the UID property.<a href="#section-9.1-1.12.1" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.2">By default, the property value points to another calendar
              component that has a PARENT relationship to the referencing
              object.  The RELTYPE property parameter is used to either
              explicitly state the default PARENT relationship type to the
              referenced calendar component or to override the default PARENT
              relationship type and specify either a CHILD or SIBLING
              relationship or a temporal relationship.<a href="#section-9.1-1.12.2" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.3">The PARENT relationship indicates that the calendar
              component is a subordinate of the referenced calendar component.
              The CHILD relationship indicates that the calendar component is a
              superior of the referenced calendar component.  The SIBLING
              relationship indicates that the calendar component is a peer of
              the referenced calendar component.<a href="#section-9.1-1.12.3" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.4">To preserve backwards compatibility, the value type <span class="bcp14">MUST</span>
              be UID when the PARENT, SIBLING, or CHILD
              relationships are specified.<a href="#section-9.1-1.12.4" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.5">The FINISHTOSTART, FINISHTOFINISH, STARTTOFINISH, or STARTTOSTART
              relationships define temporal relationships, as specified in the
              RELTYPE parameter definition.<a href="#section-9.1-1.12.5" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.6">The FIRST and NEXT define ordering relationships between
              calendar components.<a href="#section-9.1-1.12.6" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.7">The DEPENDS-ON relationship indicates that the current
              calendar component depends on
              the referenced calendar component in some manner. For example,
              a task may be blocked waiting on the other, referenced, task.<a href="#section-9.1-1.12.7" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.8">The REFID and CONCEPT relationships establish a reference
              from the current component to the referenced component.<a href="#section-9.1-1.12.8" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.9">Changes to a calendar component referenced by this property can
              have an implicit impact on the related calendar component.  For
              example, if a group event changes its start or end date or time,
              then the related, dependent events will need to have their start
              and end dates and times changed in a corresponding way.  Similarly, if a
              PARENT calendar component is canceled or deleted, then there is
              an implied impact to the related CHILD calendar components.  This
              property is intended only to provide information on the
              relationship of calendar components.<a href="#section-9.1-1.12.9" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.10">Deletion of the target component, for example, the target
              of a FIRST, NEXT, or temporal relationship, can result in broken
              links.<a href="#section-9.1-1.12.10" class="pilcrow">¶</a></p>
<p id="section-9.1-1.12.11">It is up to the target calendar system to maintain any
              property implications of these relationships.<a href="#section-9.1-1.12.11" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.13">Format Definition:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.14">
            <p id="section-9.1-1.14.1" class="keepWithNext">
                  This property is defined by the following notation:<a href="#section-9.1-1.14.1" class="pilcrow">¶</a></p>
<div id="section-9.1-1.14.2">
<pre class="lang-abnf sourcecode">
   related    = "RELATED-TO" relparam ":"
                            ( text / ; for VALUE=UID
                              uri /  ; for VALUE=URI
                              text ) ; for VALUE=TEXT or default
                CRLF

   relparam   = ; the elements herein may appear in any order,
                ; and the order is not significant.
                [";" "VALUE" "=" ("UID" /
                                  "URI" /
                                  "TEXT")]
                [";" reltypeparam]
                [";" gapparam]
                *(";" other-param)
</pre><a href="#section-9.1-1.14.2" class="pilcrow">¶</a>
</div>
</dd>
          <dd class="break"></dd>
<dt id="section-9.1-1.15">Example:</dt>
          <dd style="margin-left: 1.5em" id="section-9.1-1.16">
            <p id="section-9.1-1.16.1" class="keepWithNext">
                  The following are examples of this property.<a href="#section-9.1-1.16.1" class="pilcrow">¶</a></p>
<div id="section-9.1-1.16.2">
<pre class="sourcecode">
  RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com

  RELATED-TO:19960401-080045-4000F192713-0052@example.com

  RELATED-TO;VALUE=URI;RELTYPE=STARTTOFINISH:
   https://example.com/caldav/user/jb/cal/
   19960401-080045-4000F192713.ics
</pre><a href="#section-9.1-1.16.2" class="pilcrow">¶</a>
</div>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
</section>
</div>
<section id="section-10">
      <h2 id="name-security-considerations">
<a href="#section-10" class="section-number selfRef">10. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-10-1">
        All of the security considerations of <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-7" class="relref">Section 7</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span> apply to this specification.<a href="#section-10-1" class="pilcrow">¶</a></p>
<p id="section-10-2">
       Applications using the LINK property need to be aware of the risks
       entailed in using the URIs provided as values. See <span><a href="https://www.rfc-editor.org/rfc/rfc3986#section-7" class="relref">Section 7</a> of [<a href="#RFC3986" class="xref">RFC3986</a>]</span> for
       a discussion of the security considerations relating to URIs.<a href="#section-10-2" class="pilcrow">¶</a></p>
<p id="section-10-3">
        In particular, note Section <span><a href="https://www.rfc-editor.org/rfc/rfc3986#section-7.1" class="relref">7.1</a> (<a href="https://www.rfc-editor.org/rfc/rfc3986#section-7.1" class="relref">Reliability and Consistency</a>)</span> of <span>[<a href="#RFC3986" class="xref">RFC3986</a>]</span>,
 which points out the lack of a stability
        guarantee for referenced resources.<a href="#section-10-3" class="pilcrow">¶</a></p>
<p id="section-10-4">
        When the value is an XML-REFERENCE type, the targeted data is an XML document
        or portion thereof. Consumers need to be aware of the security issues
        related to XML processing -- in particular, those related to XML entities.
        See <span><a href="https://www.rfc-editor.org/rfc/rfc4918#section-20.6" class="relref">Section 20.6</a> of [<a href="#RFC4918" class="xref">RFC4918</a>]</span>. Additionally, note that
        the reference may be invalid or become so over time.<a href="#section-10-4" class="pilcrow">¶</a></p>
<p id="section-10-5">
        The CONCEPT and redefined RELATED-TO properties have
        the same issues in that values may be URIs.<a href="#section-10-5" class="pilcrow">¶</a></p>
<p id="section-10-6">
        Extremely large values for the GAP parameter may lead to
        unexpected behavior.<a href="#section-10-6" class="pilcrow">¶</a></p>
</section>
<div id="iana_considerations">
<section id="section-11">
      <h2 id="name-iana-considerations">
<a href="#section-11" class="section-number selfRef">11. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<div id="property_registrations">
<section id="section-11.1">
        <h3 id="name-icalendar-property-registra">
<a href="#section-11.1" class="section-number selfRef">11.1. </a><a href="#name-icalendar-property-registra" class="section-name selfRef">iCalendar Property Registrations</a>
        </h3>
<p id="section-11.1-1">
          The following iCalendar property names have been added to
          the iCalendar "Properties" registry defined in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-8.3.2" class="relref">Section 8.3.2</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>.  IANA has also added a
          reference to this document, where the properties originally defined in
          <span>[<a href="#RFC5545" class="xref">RFC5545</a>]</span> have been updated by this document.<a href="#section-11.1-1" class="pilcrow">¶</a></p>
<table class="center" id="table-1">
          <caption><a href="#table-1" class="selfRef">Table 1</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Property</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">CONCEPT</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#concept" class="xref">Section 8.1</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">LINK</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#link" class="xref">Section 8.2</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">REFID</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#refid" class="xref">Section 8.3</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">RELATED-TO</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <span>[<a href="#RFC5545" class="xref">RFC5545</a>], <a href="https://www.rfc-editor.org/rfc/rfc5545#section-3.8.4.5" class="relref">Section 3.8.4.5</a></span>; RFC 9253, <a href="#related-to" class="xref">Section 9.1</a>
</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="property_parameter_registrations">
<section id="section-11.2">
        <h3 id="name-icalendar-property-paramete">
<a href="#section-11.2" class="section-number selfRef">11.2. </a><a href="#name-icalendar-property-paramete" class="section-name selfRef">iCalendar Property Parameter Registrations</a>
        </h3>
<p id="section-11.2-1">
          The following iCalendar property parameter names have been added to
          the iCalendar "Parameters" registry defined in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-8.3.3" class="relref">Section 8.3.3</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>.<a href="#section-11.2-1" class="pilcrow">¶</a></p>
<table class="center" id="table-2">
          <caption><a href="#table-2" class="selfRef">Table 2</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Parameter</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">GAP</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#gap" class="xref">Section 6.2</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">LINKREL</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#linkrel" class="xref">Section 6.1</a>
</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="value_data_types_registrations">
<section id="section-11.3">
        <h3 id="name-icalendar-value-data-type-r">
<a href="#section-11.3" class="section-number selfRef">11.3. </a><a href="#name-icalendar-value-data-type-r" class="section-name selfRef">iCalendar Value Data Type Registrations</a>
        </h3>
<p id="section-11.3-1">
          The following iCalendar property parameter names have been added to
          the iCalendar "Value Data Types" registry defined in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-8.3.4" class="relref">Section 8.3.4</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>.<a href="#section-11.3-1" class="pilcrow">¶</a></p>
<table class="center" id="table-3">
          <caption><a href="#table-3" class="selfRef">Table 3</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Value Data Type</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">XML-REFERENCE</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_value_data_types" class="xref">Section 7</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">UID</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_value_data_types" class="xref">Section 7</a>
</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
<div id="reltype_value_registrations">
<section id="section-11.4">
        <h3 id="name-icalendar-reltype-value-reg">
<a href="#section-11.4" class="section-number selfRef">11.4. </a><a href="#name-icalendar-reltype-value-reg" class="section-name selfRef">iCalendar RELTYPE Value Registrations</a>
        </h3>
<p id="section-11.4-1">
          The following iCalendar "RELTYPE" values have been added to
          the iCalendar "Relationship Types" registry defined in <span><a href="https://www.rfc-editor.org/rfc/rfc5545#section-8.3.8" class="relref">Section 8.3.8</a> of [<a href="#RFC5545" class="xref">RFC5545</a>]</span>.<a href="#section-11.4-1" class="pilcrow">¶</a></p>
<table class="center" id="table-4">
          <caption><a href="#table-4" class="selfRef">Table 4</a></caption>
<thead>
            <tr>
              <th class="text-left" rowspan="1" colspan="1">Relationship Type</th>
              <th class="text-left" rowspan="1" colspan="1">Status</th>
              <th class="text-left" rowspan="1" colspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">CONCEPT</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#additional_new_reltype_values" class="xref">Section 5</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">DEPENDS-ON</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#additional_new_reltype_values" class="xref">Section 5</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">FINISHTOFINISH</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_temporal_reltype_values" class="xref">Section 4</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">FINISHTOSTART</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_temporal_reltype_values" class="xref">Section 4</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">FIRST</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#additional_new_reltype_values" class="xref">Section 5</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">NEXT</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#additional_new_reltype_values" class="xref">Section 5</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">REFID</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#additional_new_reltype_values" class="xref">Section 5</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">STARTTOFINISH</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_temporal_reltype_values" class="xref">Section 4</a>
</td>
            </tr>
            <tr>
              <td class="text-left" rowspan="1" colspan="1">STARTTOSTART</td>
              <td class="text-left" rowspan="1" colspan="1">Current</td>
              <td class="text-left" rowspan="1" colspan="1">
                <a href="#new_temporal_reltype_values" class="xref">Section 4</a>
</td>
            </tr>
          </tbody>
        </table>
</section>
</div>
</section>
</div>
<section id="section-12">
      <h2 id="name-references">
<a href="#section-12" class="section-number selfRef">12. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-12.1">
        <h3 id="name-normative-references">
<a href="#section-12.1" class="section-number selfRef">12.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03" class="refDate">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3986">[RFC3986]</dt>
        <dd>
<span class="refAuthor">Berners-Lee, T.</span>, <span class="refAuthor">Fielding, R.</span>, and <span class="refAuthor">L. Masinter</span>, <span class="refTitle">"Uniform Resource Identifier (URI): Generic Syntax"</span>, <span class="seriesInfo">STD 66</span>, <span class="seriesInfo">RFC 3986</span>, <span class="seriesInfo">DOI 10.17487/RFC3986</span>, <time datetime="2005-01" class="refDate">January 2005</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3986">https://www.rfc-editor.org/info/rfc3986</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4918">[RFC4918]</dt>
        <dd>
<span class="refAuthor">Dusseault, L., Ed.</span>, <span class="refTitle">"HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)"</span>, <span class="seriesInfo">RFC 4918</span>, <span class="seriesInfo">DOI 10.17487/RFC4918</span>, <time datetime="2007-06" class="refDate">June 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4918">https://www.rfc-editor.org/info/rfc4918</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5234">[RFC5234]</dt>
        <dd>
<span class="refAuthor">Crocker, D., Ed.</span> and <span class="refAuthor">P. Overell</span>, <span class="refTitle">"Augmented BNF for Syntax Specifications: ABNF"</span>, <span class="seriesInfo">STD 68</span>, <span class="seriesInfo">RFC 5234</span>, <span class="seriesInfo">DOI 10.17487/RFC5234</span>, <time datetime="2008-01" class="refDate">January 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5234">https://www.rfc-editor.org/info/rfc5234</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5545">[RFC5545]</dt>
        <dd>
<span class="refAuthor">Desruisseaux, B., Ed.</span>, <span class="refTitle">"Internet Calendaring and Scheduling Core Object Specification (iCalendar)"</span>, <span class="seriesInfo">RFC 5545</span>, <span class="seriesInfo">DOI 10.17487/RFC5545</span>, <time datetime="2009-09" class="refDate">September 2009</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5545">https://www.rfc-editor.org/info/rfc5545</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7986">[RFC7986]</dt>
        <dd>
<span class="refAuthor">Daboo, C.</span>, <span class="refTitle">"New Properties for iCalendar"</span>, <span class="seriesInfo">RFC 7986</span>, <span class="seriesInfo">DOI 10.17487/RFC7986</span>, <time datetime="2016-10" class="refDate">October 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7986">https://www.rfc-editor.org/info/rfc7986</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8174">[RFC8174]</dt>
        <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8288">[RFC8288]</dt>
        <dd>
<span class="refAuthor">Nottingham, M.</span>, <span class="refTitle">"Web Linking"</span>, <span class="seriesInfo">RFC 8288</span>, <span class="seriesInfo">DOI 10.17487/RFC8288</span>, <time datetime="2017-10" class="refDate">October 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8288">https://www.rfc-editor.org/info/rfc8288</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="W3C.REC-skos-reference-20090818">[W3C.REC-skos-reference-20090818]</dt>
        <dd>
<span class="refAuthor">Miles, A.</span> and <span class="refAuthor">S. Bechhofer</span>, <span class="refTitle">"SKOS Simple Knowledge Organization System Reference"</span>, <span class="seriesInfo">W3C Recommendation REC-skos-reference-20090818</span>, <time datetime="2009-08-18" class="refDate">18 August 2009</time>, <span>&lt;<a href="https://www.w3.org/TR/2009/REC-skos-reference-20090818">https://www.w3.org/TR/2009/REC-skos-reference-20090818</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="W3C.REC-xptr-framework-20030325">[W3C.REC-xptr-framework-20030325]</dt>
        <dd>
<span class="refAuthor">Grosso, P.</span>, <span class="refAuthor">Maler, E.</span>, <span class="refAuthor">Marsh, J.</span>, and <span class="refAuthor">N. Walsh</span>, <span class="refTitle">"XPointer Framework"</span>, <span class="seriesInfo">W3C Recommendation REC-xptr-framework-20030325</span>, <time datetime="2003-03-25" class="refDate">25 March 2003</time>, <span>&lt;<a href="https://www.w3.org/TR/2003/REC-xptr-framework-20030325">https://www.w3.org/TR/2003/REC-xptr-framework-20030325</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="W3C.WD-xptr-xpointer-20021219">[W3C.WD-xptr-xpointer-20021219]</dt>
      <dd>
<span class="refAuthor">DeRose, S.</span>, <span class="refAuthor">Maler, E.</span>, and <span class="refAuthor">R. Daniel</span>, <span class="refTitle">"XPointer xpointer() Scheme"</span>, <span class="seriesInfo">W3C WD WD-xptr-xpointer-20021219</span>, <time datetime="2002-12-19" class="refDate">19 December 2002</time>, <span>&lt;<a href="http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219">http://www.w3.org/TR/2002/WD-xptr-xpointer-20021219</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-12.2">
        <h3 id="name-informative-references">
<a href="#section-12.2" class="section-number selfRef">12.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC4791">[RFC4791]</dt>
        <dd>
<span class="refAuthor">Daboo, C.</span>, <span class="refAuthor">Desruisseaux, B.</span>, and <span class="refAuthor">L. Dusseault</span>, <span class="refTitle">"Calendaring Extensions to WebDAV (CalDAV)"</span>, <span class="seriesInfo">RFC 4791</span>, <span class="seriesInfo">DOI 10.17487/RFC4791</span>, <time datetime="2007-03" class="refDate">March 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4791">https://www.rfc-editor.org/info/rfc4791</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8607">[RFC8607]</dt>
      <dd>
<span class="refAuthor">Daboo, C.</span>, <span class="refAuthor">Quillaud, A.</span>, and <span class="refAuthor">K. Murchison, Ed.</span>, <span class="refTitle">"Calendaring Extensions to WebDAV (CalDAV): Managed Attachments"</span>, <span class="seriesInfo">RFC 8607</span>, <span class="seriesInfo">DOI 10.17487/RFC8607</span>, <time datetime="2019-06" class="refDate">June 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8607">https://www.rfc-editor.org/info/rfc8607</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<section id="appendix-A">
      <h2 id="name-acknowledgements">
<a href="#name-acknowledgements" class="section-name selfRef">Acknowledgements</a>
      </h2>
<p id="appendix-A-1">
        The author would like to thank the members of CalConnect,
        the Calendaring and
        Scheduling Consortium technical committees, and the following
        individuals for contributing their ideas, support, and comments:<a href="#appendix-A-1" class="pilcrow">¶</a></p>
<p id="appendix-A-2">
        <span class="contact-name">Adrian Apthorp</span>, <span class="contact-name">Cyrus Daboo</span>,
 <span class="contact-name">Marten Gajda</span>, and <span class="contact-name">Ken Murchison</span><a href="#appendix-A-2" class="pilcrow">¶</a></p>
<p id="appendix-A-3">
        The author would also like to thank CalConnect and the Calendaring and
        Scheduling Consortium for advice with this specification.<a href="#appendix-A-3" class="pilcrow">¶</a></p>
</section>
<div id="authors-addresses">
<section id="appendix-B">
      <h2 id="name-authors-address">
<a href="#name-authors-address" class="section-name selfRef">Author's Address</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Michael Douglass</span></div>
<div dir="auto" class="left"><span class="org">Bedework</span></div>
<div dir="auto" class="left"><span class="street-address">226 3rd Street</span></div>
<div dir="auto" class="left">
<span class="locality">Troy</span>, <span class="region">NY</span> <span class="postal-code">12180</span>
</div>
<div dir="auto" class="left"><span class="country-name">United States of America</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:mdouglass@bedework.com" class="email">mdouglass@bedework.com</a>
</div>
<div class="url">
<span>URI:</span>
<a href="https://bedework.com" class="url">https://bedework.com</a>
</div>
</address>
</section>
</div>
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